Thursday, June 26, 2014

Last week, Marcus came in from four days of fieldwork in the Naseby Greensand, and started lugging in box after box and bag after bag of fossils and sediment. He seemed pretty excited - unusually excited considering he had just returned (normally I'd be a bit tired and would need some recovery time at home), and he proclaimed that he had collected a bunch more shark teeth and a penguin skeleton.

After a couple of hours, Marcus had laid most of his finds on a number of trays on the museum table. Here, Marcus, Ewan, and Tsai examine Naseby specimens at tea time.

Some of Marcus' shark and fish teeth - an odontaspid sand tiger (big tooth with cusplets) and a possible cutlass fish, Trichiurus (large black triangular tooth). This photo is horribly out of focus, but I did not want to ask Marcus to take out all of his specimens again just for a marginally better photo.

Marcus also brought back some rather large chunks of amber - on the previous visit I found a smallish piece about the size of a large corn kernel (my first piece of amber ever!); this one was about the size of a donut hole.Amber, for the uninitiated, is fossilized tree sap/resin.

Chunks o' penguin - at least two humeri, a partial tibiotarsus, an ulna, pedal phalanges, and a half dozen vertebrae or so are represented.

Here's the proximal end of the left humerus - as you can see, this is a pretty damn big bird. This humerus is pretty incomplete...

...but the other humerus is virtually complete. The right humerus is in several pieces, but can be easily glued back together once dried. Provisionally speaking, this humerus is similar in size and morphology to the recently described giant penguin Kairuku, but obviously preparation is necessary to tell for sure.

Marcus and Ewan discussing the weekend's bounty, and Sophie determining the best course of preparation for the material. Marcus is thinking seriously about continuing this project into a Master's project and describing the vertebrate assemblage; he's got his work cut out for him! It reminds me quite a bit of my first research project - going to a virtually unstudied exposure of the Purisima Formation in California, collecting every vertebrate fossil, and publishing (nearly) every specimen. The best part is that Marcus was still unsatisfied with this rather large haul, and went out last weekend and brought back even more shark teeth, and found a phosphatic tooth-rich bonebed horizon that is fairly densely fossiliferous. We may be going on a field trip there next week sometime.

Wednesday, June 25, 2014

I haven't had much opportunity for field work in the past year or so. Our lab was fairly active during my first year and a half of studies here, but we got to the point where too many plaster jackets had accumulated in various places, and we didn't have any room to add any more. During my first year, on one single visit to a quarry in South Canterbury, in less than two hours we found a penguin skeleton, two dolphin skeletons, a fragmentary dolphin mandible, and two (or three?) very partial baleen whale skeletons. We had to return two more times to successfully excavate and jacket everything. The two dolphin skeletons have finally - in the last month - been exposed in the lab, and the less spectacular of the two has a partial skull with a more or less complete braincase, associated teeth, and postcrania; the other specimen is a virtually complete skeleton with skull, mandibles, teeth, tympanic bullae, periotic, most of the vertebral column, complete left and right forelimbs, and ribs. In comparison with much of the other material we have here, it is one of the most complete odontocetes we have - and probably one of the most (if not the most) complete fossil odontocetes from the Oligocene, anywhere. My adviser, Ewan Fordyce, recently received funding for a preparation "triage" for unopened plaster jackets; this recently collected material has all been dealt with, and now our preparators are beginning to open jackets from 2010. One enormous, ~2.5 meter long jacket with much of a baleen whale skull inside remains to be opened, but it is very promising progress on a rather large backlog of unprepared material.

So, when I got the invitation from undergraduate Marcus Richards (B.Sc. Honors) to go out to his field area in North Otago in the Kyeburn area (with the prospect of finding some Oligocene shark teeth and to help dig out a big teleost skeleton he had found) - I jumped at the opportunity. Marcus is doing a study of the stratigraphy, age, and paleontology of the Naseby Greensand - a stratigraphic unit of probable late Oligocene age that is thought to be a lateral equivalent of the Kokoamu Greensand a bit further north. The Kokoamu Greensand is generally mapped north of the Kakanui Range - an east/west oriented mountain range that meets the sea about an hour's drive north of Dunedin, near the sleepy town of Palmerston. On the south side of the Kakanui Range, similar greensand occurs but without the overlying Otekaike Limestone, and it is thought to be closer to shore; here it is mapped as the Naseby Greensand, it is considerably less well understood, probably because the outcrops are fewer, less spectacular, and generally more difficult to access than those in the Waitaki Valley region. A few weeks prior, Marcus had brought in a handful of fragments he had collected, including a couple of flat bones, a couple vertebrae, and a large dentary with well-preserved needle-like teeth. He indicated there was more left in the hillside, and that it could be quite large. The vertebrae were similar in size to modern fish approaching two meters in length - and this fish could easily be the size of a modern enormous tuna or small swordfish.

We unfortunately don't have many photos from the first day, so a quick synopsis is necessary. Marcus, postdoctoral teaching fellow Uwe Kaulfuss (a paleobotanist/paleoecologist), my wife Sarah, and I drove out to the locality, stopping three different times for coffee at Uwe's insistence (I thought I was a coffee freak). It was forecasted to be one of the last nice days before winter really set in, and it was in fact the official first day of winter in NZ. In the sun, it was about 10-12C (50-54 F for American readers back home), so not frigid, but not toasty by any means either. I generally have a difficult time in any weather over 75 F (~24C) anyway, so this was actually optimal. Marcus showed us the spot where the fossil fish was: up on a hillside, with a small cliff below. The cliff was steep enough to prevent us from walking directly uphill to it, requiring us to hike down to it from above through tussock grass, which is a bit awkward to walk through since you can't see the ground where your feet are planting - a bit alarming when you're within a few feet of a ten foot drop. We spent most of the day collecting the few bits that were exposed on the surface, digging a trench the fossil, uncovering more bones (by accident) in the trench and bagging up those, and eventually getting the fossil into a condition ready to jacket. During the excavation we bagged up another half dozen vertebrae and what looks to be a partial skull. At 4pm the sun went down, and my hands went into icy water to start mixing the plaster (by the way, if you are ever digging in a spot where you need to get water up a steep incline and don't want to risk hauling it up in a bucket that can spill - just pour the water into a large freezer ziplock bag, it works great). The water was straight out of the river below and was so unbelievably cold. As the sun went down over the hill, we felt the air temperature drop to about 0C (32F) within five minutes. Marcus, Uwe, and myself worked quickly to apply the jacket, clean up, and leave. A return to the locality would be necessary - soon - in order to remove the jacket before it just got too damn cold to do anything about it.

Four days later Marcus, Tsai, and I returned to the locality to finish the excavation. In this photo of Marcus and I you can see the vertical face just a few feet behind Marcus, which originally was an even slope until we chopped a big ledge into the hillside.

There was a pretty nice view looking north towards Dansey's Pass. And yes, that's snow. There should even be more of it this time of year. Matter of fact, the first day, the road was still closed because of a snowstorm that blocked the pass (further up the road, of course) so we had to park and walk up about two kilometers. When we returned, the road was opened again and Marcus drove to within about 100 meters of the excavation site.

Marcus eventually got fed up with having to hike way around the hill, so he carved in a handful of precarious footholds for a more direct ascent from the spot at the bottom of the hill where we kept most of our gear.

Within a half hour we had flipped the jacket over and began trimming it down. Prior to trimming, the jacket weighed well over 150 pounds or so - not enormous, but far larger than it had to be. As it turned out, the bedding here was also near vertical or perhaps around a 60 to 70 degree angle - so the bedding plane with the fossils was actually exposed on the side of the pedestal. We began "carefully" scraping rock out of the opposite side, working our way down to the ~4-6" thick zone where disarticulated fish bones were known to be present. Here Tsai and Marcus are working on the final trimming. We had to cut away about 10" of empty plaster jacket siding after removing rock from the jacket. The rock, by the way, was this wonderfully compliant lightly consolidated muddy greensand and very easy to dig through. Although the others were a bit skeptical and thought we risked damaging the bone, I insisted that we scrape it down until we get to the bone layer, leaving a 4" thick "surfboard" of rock inside a relatively light and easy to remove jacket. There is nothing worse than having a jacket that is too difficult to safely lift. Also, there was another safety concern nagging at the back of my mind...

Generally it's best to use paper towel as a separator. Without a separator, the plaster will stick directly to the rock and bone alike and become a complete pain to remove. Newspaper works fine, but occasionally ink can be transferred onto the specimen. The first day we had forgotten to bring anything for wrapping small fossils or as a separator, so Marcus had to run back to the Dansey's Pass Coach Inn and see if they could spare some toilet paper and newspaper (which they did, and we were very greatful for it). In the past decade, I've also learned that a camelback not only keeps you hydrated, but is an excellent way to get a nice coat of water onto a separator like paper towel or newsprint. If you put on the separator dry, the wind will often just blow it away; it's also easier to get it to conform to the shape of the rock pedestal if it's damp.

That's some cold river water. This time, we started jacketing at about 2pm.

Marcus and I putting the final touches onto the opposite side of the jacket.

And that about does it - after a bit of waiting, we had to figure out how to remove the jacket. That morning I inquired with various geology staff whether or not anyone had a cargo net - an odd question, but we have so much random equipment here you never know and might as well ask. Unfortunately, that was one piece of equipment nobody seemed to have. I wanted to lower the fossil down the hillside rather than haul it up and over - which would be a nightmare. The rock is soft enough that unless considerable effort went into carving steps, that much weight would just result in someone sliding. Watching a carefully made jacket with a priceless specimen inside bouncing down a hillside and bursting apart is one of my worst nightmares.

While we were unable to find a cargo net, I did find an alternative...

In the paleo equipment storage room, we've got an unusually thick burlap sack (or hessian sacks as they call them here) that's usually used as something to put the chainsaw on top of when out in the field. I figured that if we could put the jacket inside of it, we could tie ropes to it and carefully lower it down the hillside.

Fortunately, the jacket was just small enough to be slipped inside the burlap sack. Unfortunately, the burlap sack (like most) does not have brass grommets, so in order to tie ropes to the sack, I used an old trick I learned in my days in boy scouts: find a small rock from the river below, stick it into the corner at the opening, pull the burlap tight around the rock, and then tie the rope around the neck of the "pouch" that the rock is sitting in: the rock is wider than the rope knot, and cannot leave the small pouch you've made.

It worked like a charm.

I was actually surprised at how light the jacket was - it took barely any effort at all to control it as it went down the hillside.

And, the best part is, we made it into the car at around 4pm just around when the sun went behind the hill. Here's Marcus with his prized catch inside, ready for the two hour trip back to town. We're really looking forward to seeing what is inside the jacket, and for having the other fish bits that we collected during the trenching process prepared.

Thursday, June 12, 2014

I recently saw a news piece on KQED.com about some middle Miocene marine mammal fossils being found during the repairs and construction going on with the Calaveras Dam in the east bay (East San Francisco Bay area, that is). Few marine mammal fossils have been collected from the east side of the bay in the last 75 years thanks to extensive overgrowth and proliferation of paleontologically unmitigated construction, so I was pretty happy to hear about this.

The fossils include baleen whales, desmostylian remains, and even Carcharocles megalodon teeth, above. The deposit is apparently mapped as being part of the Temblor Formation - I had no idea it was mapped as far north as the bay area, and am wondering if its not some local lateral equivalent.

East Bay Regional Park personnel share some of the finds with visitors. From www.blogs.kqed.org.

There's some sort of baleen whale in here, and the piece sticking out is identified as an ear bone. Needless to say, my curiosity is piqued!

I'll admit now that I have known about this for a while, and am pleased that they've made a series of further discoveries. The middle Miocene is well-known from Sharktooth Hill and a couple of other localities in Southern California and Oregon, but not further north. So, it will be interesting to see if the diagnostic marine mammals are the same species seen further south - or not. I even had a discussion about these fossils with someone at SVP, and I cannot now for the life of me remember who that person was. If that person is reading this right now... please email me! Normally my memory isn't this terrible, so I apologize in advance.

Otherwise, I've sent an email to the folks in charge as I'm genuinely curious to see which museum this material is heading off to eventually.

Tuesday, June 10, 2014

Finally, we're at the last post in this series - one that I've been procrastinating on, as I knew it would be a total bear to write. But, now I'm done! Hooray. Next up after this - a recent announcement of fossil marine vertebrate discoveries in the East Bay (e.g. east San Francisco Bay Area) and some photos from a recent field excavation, or as I like to call it, going fishing in the Oligocene.

The phylogenetic position of Allodesmus

The relationships of Allodesmus
have been a serious bone of contention (pun intended…sorry) in pinniped
paleontology for several decades, and is a bit of a polarizing issue within the
field. I have my own biases which no doubt will shine through below, but will
try to show both sides of the argument. Two major camps exist within pinniped
paleontology: those in favor of pinniped diphyly and otarioid monophyly
(Otariidae + Odobenidae + Desmatophocidae + enaliarctines), and those who
embrace pinniped monophyly and phocoid monophyly (Phocoidea is a
Desmatophocidae + Phocidae clade).

A handy hand drawn phylogenetic tree with illustrations of skulls. From Barnes et al. (1985). Although outdated, no subsequent illustration has ever been put together of this caliber for pinniped evolution, and I've always wanted to redo this given our substantially expanded fossil pinniped record.

Mitchell (1966) arguably represents
the first “modern” treatment of Allodesmus, and while he did not
explicitly propose any phylogenetic hypothesis for pinnipeds, herecognized that Allodesmus was quite
derived and probably not directly ancestral to living sea lions. Prior workers,
in the absence of other fossils, implicated the fragmentary remains of Allodesmus
in the ancestry of modern pinnipeds. We now know that desmatophocids were a
relatively highly derived evolutionary experiment that lasted for about 10 Ma –
and ultimately went totally extinct – and despite predating true seals (by 5
Ma), walruses (by 2-3 Ma), and fur seals and sea lions (by 10 Ma or so) –
desmatophocids evolved independently from early pinnipeds and did not give rise
to any of these modern groups. Given the sheer abundance of Allodesmus in
the mid Miocene fossil record, it is ultimately unsurprising that it was one of
the earliest discovered fossil pinnipeds; unfortunately, this also remained one
of the only well known fossil pinnipeds for quite some time, and it was not
until the 1970’s that paleontologists could make heads or tails of it.

Allodesmus was classified as
an otariid relatively early on by such researchers as Remington Kellogg,
Theodore Downs, and Victor Scheffer. Mitchell (1966) suggested some
relationship with walruses and sea lions, and erected the subfamily
Desmatophocinae to include it and Desmatophoca (and curiously, the
walrus Dusignathus) within the Otariidae (=Otarioidea of other workers).
It must be stated that during the 1960’s, 1970’s, and 1980’s, most pinniped
researchers were working under the implicit assumption that pinnipeds were
diphyletic – with walruses and sea lions sharing a common bear-like ancestor,
and true seals evolving separately from a mustelid ancestor (more on this
later).

The phylogenetic hypothesis of Barnes (1972).

Barnes (1972) recognized that
desmatophocids diversified prior to the appearance of otariids, and even
recognized that otariids were more primitive than desmatophocids in many
regards, despite diversifying long before the appearance of the earliest fossil
otariids. Barnes (1972) was appropriately skeptical that otariid ancestry had
anything to do with desmatophocids, and suggested that otariids were
secondarily derived from a primitive ancestral stock, and similarly indicated
that desmatophocids could probably not be implicated in walrus origins either.
Barnes’ (1972) proposed phylogeny can be seen above. Mitchell (1975) published
a phylogenetic hypothesis which did not differ appreciably from Barnes (1972).

The phylogenetic hypothesis of Mitchell (1975).

A later study by Repenning and
Tedford (1977) showed a more or less similar phylogeny, with desmatophocids and
odobenids sharing a more recent common ancestor than otariids. Repenning and
Tedford (1977) further agreed that no modern pinnipeds could have been derived
from the desmatophocids.

The phylogenetic hypothesis of Repenning and Tedford (1977).

New research
published by Andre Wyss in 1987 indicated the possibility that pinnipeds were not only
monophyletic (spurred by early studies of molecular phylogeny), but that
walruses and true seals (together with desmatophocids) might form a
monophyletic group (the clade Phocomorpha). As a response to this, Barnes, in
his 1989 description of the enaliarctine Pteronarctos goedertae, published
a new phylogeny for fossil and modern pinnipeds (see below). Curiously, one of
the earliest comments regarding Wyss’ hypothesis of pinniped monophyly was that
his “conclusion is contradictory to that reached by many other researchers who
have examined many of the same characters as Wyss”. Although a fair comment
here, this point has been reiterated time and again by proponents of pinniped
diphyly, in print and in person to the point where it is reminiscent of an
appeal to authority. But I digress. Barnes (1989) shows a hand-drawn cladogram
depicting otarioid relationships, and pointed out a couple of minor holes in
Wyss’ arguments, including the observation that phocids, desmatophocids, and
the enaliarctine Pinnarctidion all share a “mortised” (e.g. vertically
thickened/expanded) zygomatic arch (or cheekbone for the uninitiated). Barnes
pointed out that some odobeninae also possess this in addition to sirenians and
desmostylians, and that the convergent nature of this feature means it should
be avoided in phylogenetics. Such arguments are commonplace in vertebrate
paleontology, and the idea that certain types of characters ought to be avoided
because they are convergent is pervasive. However, the moment any character
evidence is ignored – for any reasoning – is the moment that subjectivity is
introduced into the analysis. Conversations with Jonathan Geisler back in
January 2011 opened my eyes to this, and as a result, my own philosophy is to
include as much character evidence as possible.

The phylogenetic hypothesis of Barnes (1989).

Regardless, Barnes (1989) did not
present a computer-assisted analysis, but rather listed a series of characters
supporting otarioid monophyly, and other clades within the Otarioidea. In a
non-computer assisted analysis, a hand-drawn cladogram is assembled based on
the listing of characters supporting “premeditated” clades – no testing is
involved, and it is completely subjective. The 1980’s saw the proliferation of
computer-aided cladistic analysis (referred to hereafter as just cladistic
analysis). For the uninitiated, cladistic analysis emphasizes the grouping of
organisms based on shared features rather than differences. This sort of
analysis is conducted by producing a list of characters (e.g. characteristics
or features) with different character states (e.g. conditions). An example of a
classic (and already mentioned) character for fossil pinnipeds would be:

All species
coded as ‘1’ would be grouped by the computer into a clade. In this case, the
supported clade would be the clade Phocoidea. It is possible to have more than
two character states; only derived character states (e.g. anything other than
zero) will unite species together. When an analysis includes hundreds of
characters like this, it is likely that some will be mutually exclusive: for
example, in the context of this discussion, some characters might support
otarioid monophyly and others might support phocoid or phocomorph monophyly.
What happens when two characters support mutually exclusive groups of species?
The short answer is that, as you might suspect, they cancel each other out. At
larger scales, if an analysis includes dozens of characters that support
mutually exclusive clades – they will also cancel each other out if they are of
roughly equal proportions. This can be solved by one of two ways: ignoring
characters that support a clade you don’t like, or searching for additional
characters that might support one hypothesis over another. Admittedly, the
first option sounds dangerously unscientfic (…because it is), but plenty of
paleontologists are guilty of this practice, unfortunately.

An excellent summary figure contrasting the "newly" proposed phylogeny under the "Phocomorpha hypothesis" of Berta and Wyss (1994) with the "classical" view of pinniped diphyly advocated by most earlier researchers. From Berta and Wyss (1994).

A response
to the phylogenetic hypothesis of Barnes (1989) was a large cladistic analysis
of morphological data by Berta and Wyss (1994) that still remains the only
comprehensive phylogenetic analysis of pinnipeds (as alluded to below, Morgan
Churchill and I presented an even larger analysis at the 2010 SVP meeting, but
it needs a lot more work and was a good “first stab”; comprehensive
phylogenetic analysis of pinnipeds remain a viable future research project).
This study used 143 characters including skeletodental, soft tissue, and even
behavioral characters. Berta and Wyss (1994) found strong support for a
monophyletic Pinnipedia, monophyly of the Phocomorpha (walruses +
desmatophocids + true seals), and monophyly of the Phocoidea (Desmatophocidae +
true seals + Pinnarctidion). Berta and Wyss (1994) identified that the
sheer majority of purported synapomorphies for the Otarioidea also occurred in
terrestrial arctoids (indicating that they are primitively present in
“otarioids” and are thus not phylogenetically informative), and that many other
features are also present in true seals (which, of course, were not considered
by Barnes because of the a priori assumption that pinnipeds are
diphyletic).

The phylogenetic hypothesis of Berta and Wyss (1994); black bars denote the number of synapomorphies for each node (I think).

A biting
response to this analysis was published less than a year later by Barnes and
Hirota (1995) who criticized the definition of a few features (some of which
were later acknowledged by Deméré and Berta, 2002, to be valid criticisms).
Barnes and Hirota (1995) made some comments on Berta and Wyss characters which
in my mind don’t make much logical sense. For example, they criticize the use
of a character based on the presence of an enlarged digastric insertion on the
mandible as it is “related to the musculature and functional morphology of the
dentary and not of phylogenetic significance” (Barnes and Hirota, 1995:356). So
what? I fail to see the distinction here: all morphological features are
influenced by function to some degree, and either characteristics have a known
function, or the function is unknown and we simply do not know enough to make
an informed statement about the functional significance of a certain feature.
The second puzzling statement is a criticism of the use of soft tissue features
by Berta and Wyss (1994), as “soft anatomical structures that are not reflected
by bone morphology cannot elucidate the relationships of fossil taxa”. While it
is true that such soft tissue features are not preserved in desmatophocids,
they are present in the walrus, which is sister to the desmatophocid + true seal
clade (Phocoidea) in the analysis of Berta and Wyss (1994). Here’s the problem
with this statement: when it comes to cladistic analysis, soft and hard tissue
characters hold no inherent value over one another: they are all equally
important according to the computer. To the computer, a soft tissue character
codable only for modern pinnipeds is no different from, say, mandibular
characteristics that can only be coded for fossil and modern species with
preserved mandibles: no distinction is made. Thus, the argument that a certain
character is irrelevant because it can only be coded for a small number of
species is erroneous. To further illustrate this, there are some skeletal
characteristics that could potentially be coded for fossil pinnipeds – if found
beautifully articulated – that can generally only be coded in modern specimens.
Subsequent studies have focused on smaller groups of pinnipeds, and not a
single morphological study since has really tested any of the larger clades
within pinnipeds – and that includes the phylogenetic position of Allodesmus as
a true seal relative.

So, where
does that leave us today? It’s now 20 years since Berta and Wyss (1994) was
published, establishing a new paradigm for pinniped phylogeny – and we are
still without a followup to it. It is an excellent paper, and I strongly
recommend that any student of pinniped evolution read it. However, there’s a
serious catch. Virtually all published studies of molecular data have
unilaterally supported an otariid-odobenid clade (Otaroidea – walruses and sea
lions), and also supporting pinniped monophyly. So, molecular phylogeny
suggests a bit of a compromise between the two extremes. But, molecular
analyses – like soft tissue data – are inapplicable to the question of where Allodesmus
fits in. The postcranial skeleton of Allodesmus is very similar to
odobenids and otariids – while many features of the skull are more similar to
true seals. Personally, I’ll remark upon the fact that there are far fewer
skeletal features linking walruses with Phocoidea than there are supporting the
Phocoidea (desmatophocids + true seals), and I could be convinced of otarioid
monophyly if someone were to carefully identify a suite of synapomorphies. In
this context, my own suspicion is that molecular work is probably correct – but
as of yet I cannot point to much morphological evidence in support of it – and
that Allodesmus most likely, given the volume of shared features
identified by Berta and Wyss (994), does share common ancestry with the true
seals. Much, much more work is necessary to test all of these hypotheses, and I
am not particularly beholden to any idea, other than it is abundantly clear
that pinniped diphyly is an outdated concept not supported by modern science
and lacking molecular and anatomical support. Another post on pinniped diphyly
would be instructive.

Evolution of Allodesmus

Regardless of larger phylogenetic
relationships, a few comments can be said about the evolution of this fossil
pinniped are worth making. Allodesmus is the sister genus of Desmatophoca
– and if a genuinely separate genus, Atopotarus is closer yet to Allodesmus.
Desmatophoca is fairly old – the type specimen of Desmatophoca brachycephala
is perhaps as old as 21 Ma, demonstrating that desmatophocids diverged fairly
early from enaliarctines. Desmatophocids in general are noteworthy for being
the earliest large bodied pinnipeds to evolve; both species of Desmatophoca are
large, and most species of Allodesmus are even larger. Numerous changes
occurred between the evolution of Allodesmus from Desmatophoca-like
morphology (fossils from the Astoria Formation purportedly show that Desmatophoca
oregonensis and an “Allodesmine” co-occurred, thus demonstrating that the
two do not share an ancestor-descendant relationship – but this undescribed Allodesmus/Allodesmine
has yet to be described; Barnes and Hirota, 1995). Changes in the skull and
mandible include elongation of the rostrum, enlargement of the orbits,
development of a prenarial shelf, further elaboration of the “mortised” zygomatic
arch, fusion of postcanine tooth roots, simplification of tooth crowns,
elongation of the mandible, and enlargement of the posteroventral flange for
the digastric insertion of the mandible.

Curiously, Allodesmus
appears to have gone extinct by the early Messinian or late Tortonian (~9 Ma),
based on the age of the youngest known specimens from the Montesano Formation
of Washington and the Santa Margarita Sandstone near Santa
Cruz. Post-middle Miocene specimens of Allodesmus
are also relatively rare: the post-middle Miocene record is effectively
restricted to the partial skeleton from the Montesano Fm. of Washington,
about a dozen teeth from the Santa Margarita Sandstone near Santa
Cruz, and a few teeth from the Monterey Formation of
Orange County I saw at the Cooper Center
last Fall. In contrast, the late Miocene record of larger pinnipeds is
dominated by “imagotariine” and dusignathine walruses like Imagotaria, Gomphotaria,
Dusignathus, Pontolis (and two other unnamed dusignathine genera)
and the early odobenine Aivukus. Other pinnipeds include the early
otariids Pithanotaria starri and Thalassoleon. Interestingly,
early and Middle Miocene walruses (e.g. Proneotherium, Neotherium,
Pseudotaria) that co-occur with desmatophocids are mostly relatively small
bodied, similar in size to large fur seals and female sea lions (Pelagiarctos
is a notable exception, although it wasn’t very large). However, in the
late Miocene, walruses both increase in body size (the “smaller” walruses like Imagotaria
were only the size of large California sea lions, while monsters like Pontolis
were five or six meters in length – southern elephant seal sized) but also
became more diverse.

Future Directions

Clearly, the issue of the
phylogenetic position of Allodesmus amongst pinnipeds is not quite a
dead and beaten horse, rather one that has been assaulted numerous times but
failed to die. As things stand, we know barely more about the relationships of
this species than we did in 1990 – which is not to deride either side of the
debate. In my opinion, the answer has not yet been adequately addressed, and
more character evidence - and a much broader taxonomic sample - are needed.
Smaller studies with limited taxonomic sampling are inherently going to be less
adequate than broader approaches, and I think the next big step is going to be
putting together a comprehensive phylogeny of all modern and fossil pinnipeds
(at least, the ones complete enough to be useful, that is). This is something
Morgan Churchill and I are planning on in the somewhat distant future; our
first stab at this was presented on a poster at the 2010 SVP meeting in Pittsburg,
which showed a somewhat similar topology to that of the Berta and Wyss (1994)
paper. As we speak, some promising research is being done by Reagan Furbish, a
student of Annalisa Berta at San Diego
State University.
Reagan had a pretty neat poster about her Master’s thesis work on the
phylogenetic position of Allodesmus, which actually won an award for
best student poster at the Marine Mammal conference here in Dunedin
last December. Needless to say I’m really looking forward to seeing what else
she digs up.

An undescribed skull and mandible of Allodesmus sp. from the Monterey Formation, on display at the San Diego Natural History Museum. Does this represent a new species of Allodesmus? Or a previously described species? The short answer is, nobody knows (yet).

In addition to these ongoing
issues, there is a whole lot more material of Allodesmus known now. The
late Miocene Allodesmus specimen at the Burke Museum (Montesano
Formation, Washington) is still undescribed, and there are numerous isolated
teeth in collections at UCMP and the Santa
Cruz Museum representing similarly young specimens of Allodesmus from
the Santa Margarita Sandstone near Santa Cruz (the latter being an easy project
I’ll probably take on in search of “low hanging fruit”). Last fall I saw a
partial but nonetheless informative skull (with mandibles and an atlas) of Allodesmus
kernensis from Sharktooth Hill at Sierra
College; this, and other new
specimens from SDNHM (including another nice, partially disarticulated skull),
certainly warrant further study. If you read Mitchell’s (1966) paper on Allodesmus,
yeah, it’s big and thick and well illustrated, but the skull description is
actually quite brief. It’s been supplemented by the descriptions in Barnes
(1972), but more material always offers to provide new insights. Another
undescribed Allodesmus from the Monterey Formation is on display at
SDNHM. There is undescribed Sharktooth Hill Bonebed material at LACM that needs
publishing, but I can’t say more about it. Barnes and Hirota (1995) also
mention an early Miocene “allodesmine” from the Astoria Formation of all
places.

Skulls like this (Allodesmus kernensis, Sharktooth Hill Bonebed, SDNHM) are by no means as impressive as some of the previously published specimens - but even squashed, roadkill specimens like this preserve a hell of a lot of morphology and beg - no, deserve careful study.

Allodesmus has been arguably
oversplit, and the taxon is in dire need of revision. Detailed study of new
material – whether from Sharktooth Hill or beyond – will help resolve questions
of diversity, biogeography, and phylogeny.

What else can be done? The sample
from the Sharktooth Hill Bonebed alone is sufficient enough to permit studies
of variation of any number of elements (skulls, mandibles, teeth, postcrania),
in addition to providing well-preserved specimens for functional analysis
(feeding ecology, muscle attachment mapping, further studies of locomotion) and
studies of ontogeny and sexual dimorphism, as well as isotope geochemistry
(e.g. Oxygen and Carbon isotopes for studying paleoecology). There is literally
a host of avenues for future research – just on a single genus of pinniped. The
sky’s the limit – and Morgan and I can’t do all of it! I hope this reaches
someone who can help out with the California
marine mammal fossil record – there is so much more left to do, evenon the best known fossil pinniped.

L.G. Barnes. 1989. A new enaliarctine pinniped from the Astoria Formation, Oregon, and a classification of the Otariidae (Mammalia: Carnivora). Contributions in Science, Natural History Museum of Los Angeles County 403:1–26.

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the
otariid subfamily Allodesminae in the North Pacific Ocean:
Systematics and relationships. The Island
Arc3:329-360.

Thursday, June 5, 2014

An undescribed skeleton of Allodesmus from the Miocene of Japan, on display at the National Museum of Nature and Science in Tokyo.

The abundance of Allodesmus in the Neogene marine
record in concert with its completeness made investigation of its paleoecology
and life habits inevitable. However, most of what follows is scoured from a few publications, and ample scope for further studies of functional morphology, ontogeny, and sexual dimorphism exist for future researchers.

This doesn't really belong anywhere in here, but when I found this
strange photo I knew I couldn't leave it out. Ignoring the bizarre pose
and composition of the slab and the unecessarily included models, this
picture does actually give you an idea of how large Allodesmus was.

Ontogeny and Body Size

A few studies have touched upon
growth in Allodesmus, and have mostly discussed issues of age
determination rather than growth-related changes in morphology. Mitchell (1966)
briefly investigated epiphyseal fusion in Allodesmus, and found that
(unsurprisingly), in the forelimb epiphyses fused at the elbow before other
parts of the forelimb, and that in the hindlimb, fusion begins at the hip and
ankle before progressing to the knee joint (for casual readers, epiphyses are the
ends of long bones that begin as separate osteological units and later fuse to
the shaft – known as the diaphysis – the radius and ulna have a proximal
epiphysis, a distal epiphysis, and the diaphysis; the diaphysis generally
composes most of the bone).

A classic
and widely used method for age determination in pinnipeds and other marine
mammals is counting periodic growth marks in teeth in sectioned teeth under a
microscope. Additionally, in pinnipeds (and presumably other carnivores)
preserve a series of annular ridges/grooves in the root, corresponding to
periodic growth marks in the cross section of the tooth. Mitchell (1966) was
one of the earliest researchers to apply this method to fossil pinnipeds, and
sectioned teeth of Allodesmus from the Sharktooth Hill Bonebed. Although
the canines of the Allodesmus kelloggi holotype did not yield good
results owing to “varying replacement phenomena” (unclear if this refers to an in
vivo process or diagenesis), canines of similar size (and presumably root
closure) were sectioned and exhibited a minimum of 13 growth marks, suggesting
a minimum age of 13 years for Allodesmus kelloggi.

Allodesmus
kelloggi was estimated to be 2.6 meters in length by Mitchell (1966); this
is the most complete skeleton of a desmatophocid known, so other Allodesmus (=Allodesminae
of Barnes and Hirota, 1995) may be scaled from this species. It should be
pointed out here that Allodesmus kelloggi is the smallest known species
of Allodesmus. Mitchell (1966) pointed out that other specimens from
Shartooth Hill would be much larger (up to 3.35 meters), surpassing even the
Northern sea lion Eumetopias jubatus (3+ meters) in size. Taking
measurements of other skulls of Allodesmus, small body sizes for Allodesmus
sadoensis (2.1 meters) and Allodesmus packardi (2.2 meters) are
probable. A much larger body size is indicated for LACM 9723 – the largest
known Allodesmus kernensis/gracilis specimen – this individual, scaled
up from Allodesmus kelloggi, would have been 3.8 meters in length.
Lastly, the positively enormous adult rostrum of Allodesmus sinanoensis
(=Allodesmus megallos of Barnes and Hirota 1995) would have been a
whopping 4.8 meters in length! To put this in context, this would be an animal
the size of the largest male Northern Elephant Seal (Mirounga angustirostris
– 4.3-4.9 meters), and surpassed only by the Southern Elephant Seal (Mirounga
leonina – 4.2-6 meters).

Despite
having a relatively large sample size from the Sharktooth Hill Bonebed, little
investigation of sexual dimorphism has been attempted – and remains a lucrative
research topic for future researchers.

Mitchell's (1966) elephant seal-like reconstruction of Allodesmus. Although some have criticized the addition of a proboscis (Adam and Berta, 2001) I don't feel like it's such a bad call myself. However, more time looking at the structure of the prenarial shelf in this pinniped would permit me to make a more informed interpretation.

Life Restoration

This is by far the most speculative part of this post.
Mitchell (1966) hypothesized that due to the large size of Allodesmus,
and relatively short forelimbs (although that really remains to be
established), Allodesmus likely had thick layers of blubber, and further
speculated that Allodesmus lacked fur and was possibly hairless like
elephant seals. Another observation first made by Mitchell (1966) with the first
skull of Allodesmus was that it exhibited a peculiar prenarial shelf,
somewhat similar to elephant seals. Based on the size of this prenarial shelf,
and the position of muscle attachment scars, Mitchell (1966) speculated that Allodesmus
had a short proboscis like extant elephant seals. However, Berta and Adam
(2001) suggested that Allodesmus may not have a proboscis, citing as yet
unpublished research. The question of whether or not Allodesmus had a
proboscis has barely been answered, and future studies could certainly go
further.

The teeth of Allodesmus, from Mitchell (1966). J-M are classic examples of "phallic" Allodesmus cheek teeth.

Feeding Ecology

The skull of Allodesmus is quite different from many
other pinnipeds. It has one of the proportionally longest palates of any known
pinniped, fossil or modern. All of the teeth of Allodesmus are
single-rooted with bulbous, simple cheek teeth bearing a single cusp; isolated Allodesmus
teeth are frequently found by fossil collectors at Sharktooth Hill and appear
“phallic” to many amateurs (check out the photo; you can do the math). The
canines are relatively small in Allodesmus in comparison to similarly
sized otariids and odobenids (with the exception of the adult “snout” of Allodesmus
sinanoensis; =Allodesmus megallos of Barnes and Hirota, 1995). The
mandible is relatively gracile but bears a well developed flange for the
digastric insertion, as in modern elephant seals (Mirounga). Allodesmus
curiously lacks well developed nuchal and sagittal crests as in many fossil
and modern otariids and many odobenids, and also has an unusually small
coronoid process of the mandible – suggesting reduced temporalis musculature
(the temporalis is the primary jaw closing muscle; those of you who are dog
owners can feel it by petting the top of your dog’s head while it is chewing;
cat owners should not try this). Lastly, the eye sockets of Allodesmus
are proportionally enormous; they are so large, that Debey and Pyenson (2011)
suggested that Allodesmus was a deep diver, like modern elephant seals.

The lengthening of the palate is
probably related to suction feeding (Adam and Berta, 2002), and Allodesmus was
reconstructed as a pierce/raptorial feeder by Adam and Berta (2002). The
simplification of the postcanine teeth and reduction in size of the posterior
postcanine teeth suggests reduced utility of the dentition, potentially even more
so than other pinnipeds. The underdeveloped cranial crests and small coronoid
process suggests a decreased importance of jaw closing musculature relative to
many other pinnipeds. All of this, in concert with the enormous eye size and
potential deep diving ecology, in my opinion, suggests a possible suction
feeding elephant seal-like habitus. However, it is important to note that
craniodental morphology correlates poorly with diet in pinnipeds.

Allodesmus kernensis (=Allodesmus gracilis of Hirota and Barnes, 1995) at the San Diego Natural History Museum reconstructed in a very sea lion like pose. Check out the length of the forelimb - at first glance, it screams "sea lion" in terms of function.

Locomotion

Osteological characteristics of limb bones and the
hypothesized monophyletic clade formed by desmatophocids and phocids
(Phocoidea) led Berta and Adam (2001) to interpret Allodesmus as a
hindlimb-dominated swimmer. However, a subsequent study by former Gingerich
student Ryan Bebej (2009) based on proportions of limb bones identified that Allodesmus
was most similar to modern fur seals and sea lions, which are
forelimb-dominated swimmers. In fact, fur seals and sea lions swim in a
somewhat similar fashion to penguins (although have a forelimb that bends more
at the elbow). Interestingly, Allodesmus was found to be slightly less
aquatically adapted than extant pinnipeds by Bebej (2009), which is borne out
by the fact that Allodesmus first appeared within the first 10 million
years of the evolutionary history of pinnipeds. Significantly, Allodesmus has an otariid/odobenid like ankle, indicating that this pinniped could terrestrially "walk" as opposed to wriggle like modern earless seals (Phocidae). Modern true seals cannot rotate their ankle forwards, meaning their hindflippers are always pointing posteriorly and cannot be used for locomotion, and so they must wriggle around awkwardly on beaches like a kid trapped in a sleeping bag.

Biogeography

Lastly, Allodesmus is now known from the middle and
late Miocene of California, Baja California,
Washington, and Japan.
This indicates that this genus was widely distributed across much of the
Northern Pacific, including most of the west coast of North America.
Allodesmus had a circum-North Pacific distribution, paralleled with many
other Mio-Pliocene marine mammals (Desmostylus, Paleoparadoxia, Albireo,
Kentriodon, Thalassoleon, Callorhinus, Hydrodamalis,
Dusisiren, and many others), and many modern cetaceans and pinnipeds. Allodesmus
courseni (=Atopotarus of some authors) and Allodesmus kernensis are
known from both California and Japan,
suggesting that some species of Allodesmus may have enjoyed a wide
geographic range. Curiously, desmatophocids never escaped the north Pacific.
Why? My hypothesis would be that Allodesmus was cold-water adapted, and
unable to cross the warm equatorial waters that serve as a formidable thermal
barrier to north-south dispersal even today. Similarly, Allodesmus never
invaded the Atlantic, suggesting it was unable to
disperse through the Central American Seaway, although many pinnipeds and other
marine mammals were able to disperse from the western North Atlantic
to the eastern South Pacific during the Miocene.

Next up: part 4, the controversial phylogenetic position of Allodesmus,
and future directions for research.

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About the Coastal Paleontologist

I'm a paleontologist and adjunct faculty at College of Charleston in South Carolina, with research interests in Cenozoic marine vertebrates with an emphasis on marine mammals (whales, dolphins, pinnipeds, otters, sea cows, and others), but I willingly entertain brief distractions into the worlds of marine birds, sharks, and fish. My M.S. (2011, MSU-Bozeman) focused on marine vertebrate taphonomy whilst my Ph.D. (2015, U. Otago, NZ) focused on Oligocene baleen whales from New Zealand. Current research is concerned with fossil cetaceans from South Carolina including Oligocene eomysticetids, toothed mysticetes, and archaic dolphins.